The present invention relates to a system for controlling the output of an automotive engine having a traction control system.
The traction control system is employed for improving the power of the engine at a low vehicle speed. When the tires slip on a snowy road or on a wet road at starting, the vehicle can not be driven ahead or the speed of the vehicle can not be increased. In such a state, the power of the engine is effectively used by the traction control. And, the traction control is used for preventing sudden spinning of the tire while keeping steerability in order to ensure safe driving in the entire range of vehicle speed.
There have been proposed various kinds of traction control systems, and some have to reduce engine torque at a low vehicle speed, or the other systems are controlled only by braking operations.
Japanese Patent Application Laid-open 59-68537 discloses a traction control system in which engine power is controlled in accordance with slipping of wheels. Japanese Patent Application Laid-open 60-147546 discloses a system in which a limit drive torque is calculated in accordance with the friction coefficient between the road surface and wheels, and the load against the ground. The engine is controlled so as to obtain the calculated torque.
In the former system, the power of the engine is controlled by a feedback control system responsive to a slip ratio. Such a feedback system is subject to a delay in response, which causes vehicle speed to fluctuate.
In the latter system, it is necessary to detect the load against the ground and the friction coefficient between the road surface and the wheels in order to calculate the torque. However, since the load is a dynamic load during driving the vehicle and the condition of the road surface always varies, it is difficult to detect the load and friction coefficient with accuracy.